Date: Fri, 15 Oct 2021 09:52:07 +1000
From: Anthony Towns <aj@erisian.com.au>
To: Jeremy <jlrubin@mit.edu>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] On the regularity of soft forks
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On Mon, Oct 11, 2021 at 12:12:58PM -0700, Jeremy via bitcoin-dev wrote:
> > ... in this post I will argue against frequent soft forks with a single or
> minimal
> > set of features and instead argue for infrequent soft forks with batches
> > of features.
> I think this type of development has been discussed in the past and has been
> rejected.

> AJ: - improvements: changes might not make everyone better off, but we
>    don't want changes to screw anyone over either -- pareto
>    improvements in economics, "first, do no harm", etc. (if we get this
>    right, there's no need to make compromises and bundle multiple
>    flawed proposals so that everyone's an equal mix of happy and
>    miserable)

I don't think your conclusion above matches my opinion, for what it's
worth.

If you've got two features, A and B, where the game theory is:

 If A happens, I'm +100, You're -50
 If B happens, I'm -50, You're +100

then even though A+B is +50, +50, then I do think the answer should
generally be "think harder and come up with better proposals" rather than
"implement A+B as a bundle that makes us both +50".

_But_ if the two features are more like:

  If C happens, I'm +100, You're +/- 0
  If D happens, I'm +/- 0, You're +100

then I don't have a problem with bundling them together as a single
simultaneous activation of both C and D.

Also, you can have situations where things are better together,
that is:

  If E happens, we're both at +100
  If F happens, we're both at +50
  If E+F both happen, we're both at +9000

In general, I think combining proposals when the combination is better
than the individual proposals were is obviously good; and combining
related proposals into a single activation can be good if it is easier
to think about the ideas as a set. 

It's only when you'd be rejecting the proposal on its own merits that
I think combining it with others is a bad idea in principle.

For specific examples, we bundled schnorr, Taproot, MAST, OP_SUCCESSx
and CHECKSIGADD together because they do have synergies like that; we
didn't bundle ANYPREVOUT and graftroot despite the potential synergies
because those features needed substantially more study.

The nulldummy soft-fork (bip 147) was deployed concurrently with
the segwit soft-fork (bip 141, 143), but I don't think there was any
particular synergy or need for those things to be combined, it just
reduced the overhead of two sets of activation signalling to one.

Note that the implementation code for nulldummy had already been merged
and were applied as relay policy well before activation parameters were
defined (May 2014 via PR#3843 vs Sep 2016 for PR#8636) let alone becoming
an active soft fork.

Cheers,
aj